Need help with a 5 Color EDH Deck

[Coolie2]

I'm working on a 5 Color EDH Deck. I know already that I want it to have Nicol Bolas, Vraska, and Door to Nothingness, but I'm not entirely sure what the general theme should be. I was originally thinking Slivers, but the problem is that there are so many to pick from and if I make a sliver deck I might as well just make it a 60 card deck with 4x only a few slivers and some other important cards. Are there any other themes that I could go with aside from slivers that would go well with another 5 color Commander?

I looked over the list of possible 5 color commanders and picked the ones I thought were the best. Advice on which ones I should remove from the list of possibilities would be appreciated.

General Tazri
Sliver Hivelord
Maelstrom Archangel